1. Introduction
There are two extreme viewpoints regarding the development of the continental crust throughout
the history of the Earth. The first is that its volume grew by incremental extraction from the
mantle, with return flux recycling of material from the crust back into the mantle being of
second order importance. Variants of these growth models propose a smooth increase in vol-
ume, or that growth was more rapid in the Ar- chaean, in some cases involving rapid spurts of
crustal
growth Dewey
and Windley,
1981; McLennan and Taylor, 1982; Nelson and De-
Paolo, 1985; Patchett and Arndt, 1986. A second view is that the continental crust has remained
approximately constant or even decreased in vol- ume since the early Archaean Fyfe, 1976; Arm-
strong, 1981, 1991. Early Archaean rocks form only a minute proportion of the current continen-
tal volume and new crust is presently forming in volcanic arc systems. Therefore, models which
propose large volumes of early Archaean conti- nental crust require a flux of continental crustal
material back into the mantle i.e. recycling; Arm- strong, 1991. Some other models fall between
these extremes. Thus Reymer and Schubert 1987 proposed that by 3900 Ma the continental crust
had : 50 its current volume, and the rest was added since then. Whole rock isotopic data, trace
element geochemistry, the terrestrial heat budget and comparative planetology have been used as
constraints in these models. The usefulness of some of these in distinguishing Archaean crustal
growth versus recycling have been covered by several workers e.g. Armstrong, 1991; McCulloch
and Bennett, 1993, 1994; Bowring and Housh, 1995, and is also discussed below.
One constraint on crustal evolution models that has received less attention is the age spectrum of
detrital zircons in very ancient sediments e.g. Compston et al., 1987; Maas and McCulloch,
1991; Nutman et al., 1995. However, Stevenson and Patchett 1990 in a landmark paper demon-
strated the power of detrital zircon data in chart- ing the evolution of the crust, by using Hf isotope
data from 2 – 15 mg zircon aliquots from Meso- proterozoic to mid Archaean sediments. By this
means they concluded that continental crust had grown in volume during the Archaean. Using the
age spectrum of detrital zircons in very ancient sediments, the same conclusion is tentatively
reached in this paper.
Zircons are predominantly of granitic sensu lato magmatic origin, although they do grow in
some evolved gabbroic magmas and also in most lithologies during metamorphism. S-type granites
which form at least partially from older sedi- ments and rocks that have undergone partial
melting under granulite facies metamorphism or eclogite in some cases coesite 9 diamond grade
facies metamorphism still preserve zircon derived from their source and protoliths e.g. Schiøtte et
al., 1989a; Claoue´-Long et al., 1991; Paterson et al., 1992, and Phanerozoic detrital zircon popula-
tions commonly contain grains recycled from con- siderably older sialic crust e.g. Kro¨ner et al.,
1988; Ireland, 1992. This demonstrates the resis- tance of zircons to a wide range of surficial to
deep-seated lithospheric processes. Thus detrital zircons can provide information of the history of
their source region, particularly on the emplace- ment age of granitic sensu lato rocks.
Detrital zircon analyses have been undertaken on Archaean sediments throughout the world, to
look at local provenance and to help in establish- ing regional geological history e.g. Froude et al.,
1983; Dodson et al., 1988; Kinny et al., 1988; Nutman et al., 1991; Liu et al., 1992; Mueller et
al., 1992; Schiøtte et al., 1992; Nutman et al., 1996, 1997a; Mueller et al., 1998. In some of
these studies, the likely amount of ancient crust in the local provenance region was discussed, but
this data has never been pooled to form com- posite data sets for sediments of the same deposi-
tional age. Combining data sets give the potential of seeing the age composition of the continental
crust at any given time. In this paper, the age spectra of detrital zircons in sediments deposited
before 3500 Ma are used to place constraints on the volume of extremely ancient \ 3900 Ma
rocks that were present in the source regions. This provides information on the relative importance
of continental crustal growth versus recycling in the early Archaean complexes in which these sedi-
ments are located. It is then discussed whether the data is of global or only local relevance.
2. Crustal growth versus recycling models and previous constraints
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